Food and feed grains have long been the victims of the ravages of mold and other microorganisms. The quantity of grain which is destroyed through the actions of mold in the United States alone reaches well into the many millions of bushels. It has been estimated that fifteen to twenty percent of the corn crop alone is rendered useless for food and feed purposes due to the growth of various molds thereon during the storage of the corn. The problem is even greater if one considers the destruction of food grains on a worldwide basis.
The corn crop alone in the United States reaches well over several billion bushels annually. As much as eighty percent of this corn is consumed in animal feeding operations, specifically beef and dairy cattle, swine and fowl, after having been ground into finer mesh particles and mixed with other feed supplements. Perhaps the greatest single use for corn is that of feeding and fattening beef cattle. The common practice is to raise the latter on the grass ranges of the intermountain states. They are then moved toward the Midwest and East on their way to eventual slaughter and market as beef. The last step in this process is a feeding operation during which the beef cattle are fed enormous quantities of corn. This has the dual purpose of increasing weight as well as markedly improving the texture of the resulting beef. Obviously, this "feed lot" operation is based strictly on economics. The weight gain per pound of feed is the important factor.
When corn is harvested and removed from the cob, it commonly has an average moisture content coming from the field of 25.0 to 26.0% by weight, with a range from 20.0 to 29.0% by weight. In some seasons the moisture content of the whole kernels as they come from the field may be as high as 35% by weight. At these high moisture levels, corn has an excellent feed efficiency or weight gain per pound. If, however, the corn is dried to 10.0 or 12.0% moisture, the weight gain per pound or feed efficiency is markedly less. Some researchers have found it to be as much as 35% less in efficiency. If such predried corn is moistened with water to return it to say 20.0 to 29.0% moisture content and if it is then fed to beef cattle, the efficiency or weight gain per pound is not brought back to that of the undried or natural field-level moisture content corn. The reason for this is not understood, but the effect is a matter of record.
Field corn brought into the farm headquarters and kept on hand for feeding purposes, despite some drying in the field, usually has a natural moisture content of at least 20% by weight and is readily attacked by mold. In fact, in order to prevent mold from growing during storage of the corn, the moisture content must be reduced to 12.0%. Corn having a moisture content above this level supports mold growth which then grows increasingly profusely as the moisture content of the corn is increased above 12.0%. Thus, corn having a 20.0% moisture content will grow mold much more rapidly and easily than corn at 14.0% moisture.
The mold grows any place on the surface of the corn kernel. It has its greatest hold in the cracks or interstices at the germ end of the kernel. This makes it particularly difficult to inhibit, since growth can easily get started in these folds in the seed coat. Any inhibitor which is used must, therefore, penetrate into these folds.
Corn is normally stored on the farm headquarters area only after the corn has been artificially dried to reduce the moisture content to below 12.0%. This is done on the farm by means of a grain dryer installed at the farm headquarters; alternatively, the corn can be transported to a drying operation generally in a neighboring town and then brought back to the farm for storage before use during the forthcoming winter, spring and summer seasons. Obviously, this entails a considerable expense for drying and for transportation. Recently, there has also been a shortage of fuel for artificial drying.
The farmer or feed lot operator has one alternative and that is to store the corn in a large silo or enclosed tank. During such storage, yeast growth is encouraged. This rapidly uses up the available oxygen thereby preventing mold from growing. The installation of such a special silo or tank is a very expensive operation, and an expense which small farm operators hesitate to pay.
Molds growing on corn are generally the common penicillium and rhizopus varieties, although many others are also commonly found. Some molds produce significant quantities of mycotoxins. These are particularly virulent for fowl, since they show a high degree of mortality if fed on feeds made from corn which has become moldy during storage. The literature indicates also that such mycotoxins do produce effects in cattle and swine as well, particularly in the former. The result is a much reduced weight gain and frequently illness during the growing period from calf on up. Mycotoxins are also known to be highly dangerous to human beings, having produced a high percentage of illness with some indications of deaths being directly related to ingestion of larger doses of such mycotoxins obtained from using moldy grain.
The corn which is not used in animal feeding operations is consumed in processing operations. The oil is extracted during a wet milling operation, followed by separation of zein or protein from the starch. The latter is then used for making corn sugar or glycose, as well as a wide variety of dextrins. The latter and large quantities of corn starch are used industrially and in food products as well. Corn that has become moldy is virtually unusable for refining or separation into starch, protein and oil fractions.
It is evident, therefore, that the control of mold, that is, the prevention of mold growth on corn, is of utmost importance from a health standpoint as well as plain economics. For the farmer, this means being able to store the corn on his premises preferably at the natural moisture content at which he brings it from the field during harvesting and without artificial drying. If he is able to provide such storage, the cost of drying and other related costs such as transportation are thereby avoided. Of even greater importance is the feed value or weight gain per pound of the undried corn.
The foregoing discussion is directed primarily to corn but the problem also exists with respect to wheat, rice, oats, barley, rye, milo, red millet, white millet, yellow millet, and other cereal grains having a seed coat.
Recent publications indicate that attempts have been made to solve this problem with respect to corn by using propionic acid and/or acetic acid as mold inhibitors. Tests reported in an article in Feedstuffs for Mar. 5, 1971, show that corn which had been treated with a mixture of propionic acid and acetic acid and fed to dairy cattle resulted in reduced feed intake and milk fat depression and therefore left much to be desired.